1. Field of the Invention
The present invention relates to channel scanning, and more particularly, to a multiple input and multiple output (MIMO) communication apparatus and a channel scanning method thereof.
2. Description of the Prior Art
A related art wireless communication device has been developed based on audio services. However, with the increasing need for multimedia services of high quality, wireless communication devices have been recently changed to accommodate data services. In this respect, technologies for supporting high speed, high capacity wireless communication are being developed. One such technology is multiple input multiple output (MIMO).
A MIMO communication device uses an adaptive array antenna technique that electrically controls orientation using a plurality of antennas. The MIMO communication device narrows orientation in a beam shape to form a plurality of independent transmission paths. Data transmission in the MIMO communication apparatus is shown in FIG. 1.
FIG. 1 illustrates data transmission in a related art MIMO communication device.
As shown in FIG. 1, a MIMO communication device 110 processes a serial data stream in parallel, and thus splits the serial data stream into a plurality of dependent streams that are transmitted through a plurality of antennas to another MIMO communication device 120. Then, the MIMO communication device 120 decodes the dependent data streams to restore them to the original serial data stream.
Therefore, the MIMO communication device has the advantage in that its data transmission rate increases as much as the number of antennas in comparison with a conventional single input single output (SISO) communication device.
The MIMO communication device requires channel scanning to log into a specific network or to set a new network. For example, if the MIMO communication device produces an independent basic service set (IBSS) or searches for a new access point (AP) when roaming, channel scanning is first required. Particularly, channel scanning is significant for a dynamic frequency selection (DFS) technique that allows all the communication bands to use the spectrum without interference between wireless communication devices.
Such channel scanning is classified into active scanning and passive scanning. The active scanning is carried out in such a manner that the MIMO communication device transmits a frame for a channel search (hereinafter referred to as “search frame”) and receives a response frame to the search frame. The passive scanning is carried out in such a manner that each channel is on standby to receive a beacon frame, and then receives the beacon frame.
However, the related art MIMO communication device carries out sequential channel scanning for all channels in the same manner as the SISO communication apparatus. For example, in the case of active scanning, the antennas of the MIMO communication device transmit a frame for searching for one channel. In other words, for channel scanning for channels 1 to 3, the MIMO communication device carries out channel scanning for the first channel 1. At this time, the antennas of the MIMO communication device transmit the search frame for channel 1. Once channel scanning for channel 1 is finished, channel scanning for channel 2 is carried out. Likewise, once channel scanning for the channel 2 is finished, channel scanning for channel 3 is carried out.
In this way, the related art MIMO communication device having the plurality of antennas sequentially carries out scanning for all channels in the same manner as the SISO communication apparatus. However, such sequential channel scanning is inefficient.
Further, if the related art MIMO communication device is operated in the same manner as the SISO communication apparatus (for example, if the MIMO communication device transmits data destined for the SISO communication device), antennas other than the single antenna used for data transmission are idle.
In such a case, it takes much time to carry out channel scanning in the related art MIMO communication device. This may adversely affect the fast roaming or the DFS of the MIMO communication device.